Purification of coal distillation gas by-products



l. H. JONES Aug. 2s, 1934.

.PURIFICATION OF COAL DISTILLATION GAS BY-PRODUCTS Filed April 22 1931INVENTOR. fry/f? /76 J/ves.

Patented Aug. 28, 1934 l,971,78t l lerici:

PUREFHCATION OF CAL DISTILLATION GAS Blf-PRODUCTS Irvin H. Jones,Pittsburgh, Pa., assignor to The Koppers Company of Delaware, acorporation of Delaware Application April 22, 1931, Serial No. 531,979

2 Claims.

Myinvention relates to the treatment or purification of fuelgas such ascoal gas,rcoke oven gas, and the like', in preparation for consumption,and `especially to the treatment of constituents of 5 the gas recoveredtherefrom as by-products in the course of purification.

Fuel gases, such as coke oven gas, coal gas and the like, contain whenproduced, a Wide variety of chemical compounds. It is general practiceto- 'io remove certain of these compounds before utilisa-s tion of theresidual gas, some being removed because of their greater value whenseparated than as constituents of the gas and some being removedprincipally because they are undesirable 1b in the gas.

These lay-products and impurities are Vremoved from the gas by a Varietyof processes, both chemical and physical, and generally require sometreatment of a chemical nature to convert them into the most useful andvaluable form. For example, hydrocarbon light oil as scrubbed from fuelgas in the usual manner contains certain un-` saturated hydrocarbonswhich are undesirable in motor fuel, benzol, toluol and other fractionsinto which the light oil may be separated prior to utilization. Thesecompounds are removed or converted into Valuable constituents of thefinal product by Washing the light oil or fractions thereof with asuitable acid such as sulphuric 3()` acid, phosphoric acid, or the like.

y When-the acid Wash is completed, the acid or the sludge formed therebyis Withdrawn, leaving the oil in an acidic condition due to the presenceof traces of Washing acid remaining therein and of sulphonic acids andthe like formed during the Wash. This acidity is undesirable and isneutral* ized by treating the acid washed light oilfwith a suitablealkaline medium such as caustic sodaf solution. 4@ `Crude fuel gas alsocontains ammonia which is usually removedin part by cooling the gas tocon@ dense ammoniacal gas liquor. rThis gas liquor is in contact withtar or tar 'fractions during and after its condensation, and isconsequently contamnated with certain soluble constituents of the tar,especially the tar acids such as phenol and its homologues.

When gas liquor is distilled in the usual manner for recovery of a majorportion of its 5o tar` acid content remains in the ammonia still Waste.'-Discharge of such still Waste to streams or other bodies of Water isin many instances prohibited by regulations `designed to prevent thephenolic pollution of water vwhich ,may Subsc*` 1 quently constitute amunicipal VWater supply. As

ffl

(Cl. ISS- 38) it frequently happens that no other means of disposing ofthe still Waste is available or feasible, it has become increasinglynecessary to remove the tar acids from the still waste or from the gasliquor itself.

To accomplish this desired removal of tar acids, several processes ofdephenolization have been developed whereby tar acids are removed fromthe gas liquor by a suitable transfer agent, and then given up to anabsorbing medium, which is usually 65..` an alkali such as caustic soda.Various transfer agents have been employed including benzol, ammoniavapor, steam, and inert gases. A particularly efficient and economicalprocess in which phenols are removed from ammonia liquor by a hotrecirculated vapor or saturated gas is described in a copendingapplication of J. A. Shaw, Serial No. 230,570, led November 2, 1927.

Regardless of the type of transfer agent used, the tar acids react withthe alkali absorbent, for '.l example, sodium hydroxide solution, toform salts. The transfer agent is thereby at least partially purifiedfrom tar acids, and may be recirculated if desired to remove tar acidsfrom a further quantity of gas liquor. As the predominating tar acid isphenol, the salts formed in solution by the abcve-mentioned reaction maybe considered as sodium phenolate, although it is understood thatanalogous compounds of cresols and other homologues of phenol may alsobe present.

The phenolate solution may be withdrawn from the dephenolizing systemand sprung by treatment with an acid, preferably an acid gas such ascarbon dioxide or gases containing it, and the phenols thereby liberatedmay be recovered in 96' salable form. The value of these recoveredphenols offsets the cost of their recovery at least in part, but sincedephenolization is fundamentally a nuisance operation, it is essentialthat all costs be kept as 10W as possible and that the maximum 95 valuebe obtained from all reagents and products.

A preferred means of insuring economicaloperation of dephenolizingsystems is to make them as completely automatic as possible. This canreadily be done in the case of the vapor recirculation 100 `processreferred to hereinabove, for example, but

When operation is automatic or mechanically controlled, at least enoughfresh absorbent, such as caustic soda solution, must be supplied at alltimes to provide for removal of the maximum amount of tar acidscontained in the gas liquor at any time.

As the tar acid content of the gas liquor ordinarily varies over acomparatively Wide range and as it is furthermore desirable always tohave llO present an excess of absorbent, the conversion of caustic tophenolate by absorption of tar acids removed from the gas liquor seldomexceeds to In processes in which the transfer agent is recirculated,such as the vapor recirculation process, the caustic or other absorbentfor tar acids is the only reagent consumed. Its cost is in all processesan important item in the cost of dephenolization. Consequently, aconsiderable saving can be efected by further utilizing the alkalinityof the phenolate or caustic-phenolate solution. A process in which thisis done has been described by A. R. Albright in Patent No. 1,859,015.

In the Albright process, the alkalinity of phenolate orcaustic-phenolate solutions produced in the dephenoliaation of gasliquor and the like is utilized neutralizing acid-washed light oil. Bythis practice, the remarkable result is achieved that the causticconsumption for both dephenolisation and light oil puriiication is nogreater than it was previously for light oil purication alone,

the tar acids or phenols obtained by springing the solution withdrawnfrom contact with the neutralized light oil are still available insalable form to counteract the other costs of dephenolization.

However, it has been found in some instances that due to the powerfulsolvent action of phenol and phenolates, or to the hydrotropism of thelatter, certain constituents of the crude light oil are removed by thephenolate during neutralization and retained in the recovered phenols.These compounds are frequently of a resinou-s nature, and they sometimesimpair tl e value of the recovered phenols to such an extent that it isnecessary to dispose of the product recovered at a greatly reducedprice.

Furthermore, in some instances, as when the crude light oil isfractionated before p rication, it has been found that part of thephenols are given up by the phenolate to the light oil. This results inthe recovery of a decreased quantity of phenols.

It is obvious that the decrease in revenue from recovered phenolsresulting from either of these contingencies tends to offset the economyresulting from the double utilization of the caustic, and

g may therefore lead to restricted practice of dephenolization andconsequent injury to the public health.

An object of my present invention is to provide a process of treatingfuel gas whereby the recovery of by-products and the elimination ofcontaminated wastes are accomplished in a more economical and efficientmanner than has been possible heretofore.

A second Vobject of my invention is to provide a method whereby thealkalinity of caustic provided for use in the dephenolization of gasliquor is utilized as economically as possible.

Another ob-iect of my invention is to provide a process of neutralizingacid-washed light oil in two stages, in which sodium carbonate isemployed in the iirst stage.

A further object of my invention is to provide a method or utilizing thealkalinity of phenolate or caustic-phenolate solutions to neutralizeacidwashed light oil without adverse effect upon the phenols recovered.

lVIy invention has for further objects such other operative advantagesand results as are found to obtain in the process hereinafter describedand claimed.

According to my present invention, fuel gas such as coke oven gas or thelike is treated in the usual manner to remove tar, ammonia and lightoil. The ammoniacal gas liquor is dephenolized by an desired process,such as vapor recirculation or washing with benzol or other immisciblesolvents, and the tar acids originally contained therein are transferredto an alkaline absorbent with which they react to form phenolate.

The phenolate is sprung by treatment with carbon dioxide, flue gas, orthe like and the tar acids are liberated and separated from the aqueoussolution or carbonates and bicarbonates. These tar acids areuncontaminated with resins or other undesirable impurities andconsequently of a very high quality. No substantial loss is possiblebecause of their relatively low solubility in the carbonate-bicarbonatesolution.

The carbonate solution is then withdrawn from the springing tank andused to neutralize acidwashed light oil` I have found that eficientresults are obtained when the light oil has been previously washed witheither dilute or concentrated acid. The salt solution formed duringneutralization is substantially free from tar acids, and consequentlymay be withdrawn from contact with the oil and disposed of as desired.

Ii the supply or" carbonate solution from the springing of sodiumphenolate is not suflicient to jects in View, I now describe withreference to the ill' accompanying drawing a preferred method ofpracticing my improved. process of recovering and treating by-productsof fuel gas manufacture. In the drawing,

The single gure is a partially diagrammatic view, partly in elevationand partly in vertical section of apparatus suitable for the practice ofmy present invention.

Fuel gas is produced in a retort or coke oven 1, usually one of abattery of similar ovens or retcrts, and passes through an ascensionpipe 2 into a hydraulic main or collecting main 3. In this main it iscontacted with flushing liquor which cools the gas and condenses certainconstituents such as tar and xed ammonia therefrom. The 4 11 and a pipe12 into a tar extractor and reheater ff 13 in which the remainder of thetar is removed and the temperature of lrhe gas is raised somewhat. Y

The gas then passes through a pipe 14 into an ammonium sulphatesaturator l5 in which the Y ammonia remaining in the gas is removed. Thegas substantially free from tar and ammonia then passes through a pipe17, an acid separator 18 and a pipe 19 into a nal cooler 20. In thiscooler the temperature of the gas is reduced to substantially ieutralize the oil, or if for any other reason furerrtank 27 as before.the tank 36 into a trench 36 brother suitable atmospheric .temperatureby cooling liquor which may or may not be recirculated.

l The cooledl gas then passes througha pipe 21` into a light oilscrubber 22 or a seriesof such scrubbers in which the light oils suolias benzol, toluol and the like are removed. It then passes out of thelight oil scrubber through a pipe 24 for further purification or otherdisposal. v

Condensate and iiushing liquor separated from the gas in the pitchVtrapv pass from the bottom of the trap through a pipe 26 into a hotdrain tank 27. Inthis tank, tar is at least partially separated from theaqueous" liquor and is withdrawn through a pipe 28. rIvhe liquor flowsfrom the hot drain tank through a pipe 29 into a ilushing liquorcirculating tank 30. Y

From this tank 39, flushing liquor is` withdrawn by a pump 32 anddelivered through a pipe 83 which may terminate in sprays 34 or othersuitable distributing devices in the hydraulic main 3. This ilushingliquor serves .topartially cool and' condense further quantities of gas,and is returned with the condensate to the hot .drain Excess liquoroverflows from collecting means from Which it passes through a pipe 37into an ammonia liquor storage tank 38. Cooling liquor is delivered tothe primary cooler 8 through a pipe 40. This cooler may be of the director indirect type. In the present instance, the cooler 8 is of the directtype and the liquor passes downwardly through the cooler in intimatecontact with the countercurrently iiowing gas.

The liquor collects with condensate from the gas nearthe bottom of thecooler and iows through a pipe 42 into a cooling liquor circulating tank`48. From this tank, the liquor is withdrawn bya pump 44 andrecirculated through a water cooler 45 and pipe 40 intothe cooler 8 tocool further quantities of gas.

Excess cooling liquor overflows from the tank 43 into the collectingtrench 36 from which it passes Ato the ammonia liquor storage tank 38.If de sired, the tank 43 may be omitted. Recirculation and discharge ofexcess liquor are then eilected directly from a sump or well atthe-bottom of the cooler 8. Condensate from other parts `of the system,such as the exhauster and tar extractor, may be returned to the hotdrain tank 27.

In the light oil scrubber (or scrubbers) 22, light oils are absorbedfrom the gas by wash oil or scrubbing oil, which is thereby enriched.The

` enriched wash oil passes from the bottom of the scrubber 22 through apipe 47, a vapor-to-oil heat exchanger 48, a pipe 49, an oil-to-oil heatexchanger 50, a final heater 5l and a pipe 52 into a wash oil still orstripping still 54.'Y The temperature of this enriched oil is raised inthe `heat exchangers 48 and 50 and maybe further raised in the finalheater 51 a pipe 56.

The hot enriched oil passes downwardly through the still 54 incountercurrent flow with by steam admitted through 'fsteam introducedthrough va pipe 57. This steam removes the light oils from the enrichedwash oil, and vapors consisting chiefly of light oils and steam passfrom the top of the stillthrough a pipe 59. Thesevapors pass through thevaporto-oil heat exchanger 48 in which they are par-` tankand'recirculated by a pump 72 through a rated fromwater.y The water iswithdrawn from the bottom of the decanter through a Apipe 64 and thecrude light oil flows into a light oil storage tank 65.V f The strippedor debenzolized wash oil is withdrawn from the bottom ofthe still 54 anddelivered by a pump 67 through a pipe 68, the oilto-oil heat exchanger50, and a pipe 6'9 into a wash oil storage tank 76'. This oil may alsobe passed -through a decanter in which water and muck are separated fromthe oil before its entry into the tank 70, if desired', or the tank 79may itself be used as a decanter. The debenzolized wash oil is withdrawnfrom the wash oil storage pipe 73, wash oil cooler 74 and a pipe 75 overthe scrubber or scrubbers 22 wherein it absorbs light oils from furtherquantities of gas.

Ammonia liquor is withdrawn from the arnmonia liquor storage tank 38 bya pump 78 and delivered through a pipe 79 into a free ammonia still 89.The liquor passes downwardly through this still, wherein free ammoniaand other volatile constituents are removed by a countercurrent flow ofsteam or other hot vapor, and then passes from the bottom of the freestill through a pipe 8l into a surge tank 82.

A pump 83Y withdraws liquor from the tank 82 and delivers it through apipe 84 inte the ammonia liquor section or stripping section 85 oi adephenolizer 86, which in the present instance is of the vaporrecirculation type referred to hereinabove. in this section 85, taracids are removed from the liquor by a countercurrent iow of het vaporor saturated gas. The gas is thereby fouled or enriched with tar acids,and passes from the stripping section 85 of the dephenolizing` tower 86through a downcomer 87.

The dephenolized liquor substantially free from tar acids flows from thebottom of the stripping section 85 of the dephenolizer through pipe 88to a lime mixing chamber 89, which may conven iently be located beneaththe free ammonia still 89. In this` chamber, the liquor is mixed withmiik -of lime or other suitable alkaline material introduced through apipe 99, and fixed ammonia contained in the liquor is thereby liberated.

The mixture of lime and liquor may be agitated and heated when necessaryby steam admitted to the chamber 89 through a pipe 9i. The hot liquorthen overiiows from the liming chamber 89 to4 a liked ammonia still 92,where its distillation is completed by means oi steam introduced througha pipe 93.

The distilled liquor or still waste is withdrawn 130 from the bottom` oithe still 92 through a pipe 95 substantially free from ammonia and taracids, and may be discharged as desired. Vapore pass from the top of thefixed still 92 through apipe 96 into the` bottom of the free still .89through 135 which Vthey continue up\vardserving to remove free ammoniafrom further quantities of liquon The combined still vapors pass fromthe top or the free still 80 through a pipe 97 and may convenientlybe'returned to the gas stream near its M0 a blower 98 through theabsorbing sections 99 and 100 ofthe dephenolizer. In these sections, thetar acids are removed from the enriched transfer 15u agent by an alkaliabsorbent such as caustic soda solution.

Solid caustic soda, or concentrated solution withdrawn from a tank 102,is made up into a soiution o the desired strength which is usually from3% to 25%, and preferably about 10% NaOH, in a fresh caustic mixing tank103. From this tank it is withdrawn by a pump 104 and deliveredpreferably intermittently through a pipe 105 into the fresh causticsection or shot section 100 of the dephenolizer 86.

The caustic solution passes downwardly over contact material in thissection 100 in countercurrent with the recireulated vapor, from which itremoves the last traces of tar acids. The solution then passesdownwardly into the lower section or recirculating section 99 of thedephenolizer. Caustic or caustic-phenolate solution is recirculated overthis section 99 by a pump 106. The comparatively fresh caustic from theshot section 100 is mixed with the solution recirculated over thissection, and serves to refresh it.

The bulk of the tar acids is removed from the recirculated vapor in thelower section 99. Removal is completed in the shot section 100 and vaporsubstantially free from tar acids enters the stripping section 85 toremove tar acids from further quantities or gas liquor. The caustic isat least partially converted to phenolate by the absorption of tar acidsfrom the recirculated vapor, and excess phenolate or caustic-phenolatesolution overilows from the recirculatory system through a pipe 103 to aphenolate storage tank 110.

In some instances it may be preferable to have a plurality ofreoirculating sections similar to the lower section 99 describedhereinabove, and in other cases it may be preferable to omitrecirculation or" the absorbent and have as the absorbing y stage of thedephenolizer only a shot section similar to section 100. It is to beunderstood that my invention is not limited with respect to the numberof absorbing sections used in the dephenolizer, nor is it limited to theuse of gas or vapor as the transfer agent by means oi which the taracids are removed from the liquor and conveyed to the alkaline absorbentwith which they react to form phenolate.

Phenolate solution is withdrawn from the phenolate storage tank 110 by apump 111 or other suitable means and delivered through a pipe 112 into aspringing tank 113. 1n this tank the phenolate is sprung or carbonatedby carbon dioxide, flue gas, or the like, which is introduced into thespringing tank through a perforated pipe 115 or other suitabledistributing means.

The solution is kept at the desired temperature by means of a steam coil116. Carbon dioxide in the gas reacts with the phenolate to formcarbonates, usually sodium carbonate and bicarbonate, and to liberatethe tar acids which separate in a layer on top of the aqueous carbonatesolution. The tar acids are withdrawn through pipes 118 and 119 tostorage tanks (not shown) or other points of disposal. The carbonatedsolution is then withdrawn from the springing tank through a pipe 120into a carbonate storage tank 121.

Crude light oil is withdrawn from the light oil storage tank 65, as by apump 123, and delivered through a pipe 1211 into a light oil agitator125. In this agitator it is mixed with acid, such as sulphuric acid ofsuitable strength supplied from a tank 125, by a stirrer 127 or othersuitable mixing device. The acid serves to remove or convert undesirableconstituents of the crude light oil.

Other substances present after washing, such as spent acid or the sludgeformed during the acid wash, separate from the light oil and settle tothe bottom ofthe agitator 125. They are then withdrawn through a pipe128 for any desired disposal.

After withdrawal of the spent acid or sludge, the oil remaining in theagitator is somewhat acid, as stated hereinabove. To neutralize thisacidity, carbonate solution from the carbonate storage tank 121 isdelivered by a pump 129 or other suitable device through a pipe 130 intothe agitator 125 and stirred or mixed with the oil to insure adequatecontact. The carbonate reacts with the acids in the oil, forming saltswhich remain in the aqueous solution and settle to the bottom of theagitator. The salt solution may then be withdrawn through pipe 128 anddisposed or" as desired.

1i ie supply of carbonate solution from the springing tank is notsuiicient to neutralize all of the acidity in the oil, the oil is givena second alkaline wash with caustic soda solution or the like. Thissolution is made up in a tank 131 and admitted 'to the agitator throughpipe 132. In the agitator it is mixed with the oil as in the case of theprevious wash.

In this second wash, alkali is preferably supplied in excess of theamount required for neutralization of remaining traces of acid. Afterthis wash is complete, the solution which settles to the bottom of theagitator is stiil somewhat alkaline, and may be withdrawn through a pipe13e to the carbonate storage tank 121.

In that case it is mixed with further quantities oi springing-tankcarbonate solution and forms a part oi the rst alkaline wash liquor fora iurther quantity of acid-washed light oil. Alternatively, some othermeans of disposal of this partially spent alkali can loe-employed. Itmay, ior example, be used in the purification of fuel gas from acidicconstituents such as H26.

It is to be understood that the expression carbonate solution is usedhereinabove to refer to an aqueous solution obtained by carbonatingsodium phenolate solution or a solution containing sodium phenolate andsodium hydroxide, preferably with a gas containing carbon dioxide suchas flue gas. This solution may and usually does contain sodiumbicarbonate as well as sodium carbonate, and the carbonation be soconducted that conversion to sodium bicarbonate is substantiallycomplete. The solution may also contain salts of other acidicconstituents of the gas liquor or of the gas used for springing.

it is usually preferable to so operate the dephenolizing system that thecaustic-phenolate solution discharged to storage contains the equivalentof about 10% NaOH by weight. When this solution is sprung, the resultingcarbonate solution is substantially saturated at temperatures near orslightly above atmospheric, and consequently smaller volumes o liquidare handled than when more dilute solutions are employed.

'Howeven my invention is not limited to the use of solutions containingany particular concentration of sodium carbonate or bicarbonate.

In most instances, the carbonate solution withdrawn from the springingtank is suitable for immediate use in the treatment of acid-washed lightoil, as described-hereinabove, but my invention is not limited to use ofthe solution without further treatment after removal of tar acidsliberated by springing. Although the major portion of the liberated taracids is readily separated from the solution after conversion of thephenolate to carbonate (or bicarbonate) is completed, a portion of thetar acids may remain dissolved in the aqueous liquid. Since thesedissolved tar acids are not combined chemically with constituents of thesolution, they may be given up to the light oil, in which they are moresoluble, during the Washing process.

This is not necessarily a disadvantage, as the decrease in the amount oftar acids recovered is slight, and the light oil, particularly at plantsproducing motor fuel, is improved because of the known anti-knockproperties of phenols. However, tar acids dissolved in the carbonatesolution can be readily removed if desired by boiling the solution, withor Without aeration. I may also boil the solution with lime to convertbicarbonate to carbonate, or to partially or completely recausticize thesodium compounds.

When acid-washed light oil is treated with carbonate solution and thenwith a fresh caustic solution, as described hereinabove, tar acids orother acidic constituents oi the carbonate solution given up to thelight oil are removed by the subsequent wash with caustic. The causticmay then be treated for recovery of the tar acids if desired.

My invention has been described vvith particular reference to thetreatment of acid-Washed light oil With carbonate solution, with orWithout a subsequent treatment With caustic, but it is to be understoodthat an analogous treatment of acid-washed light oil fractions `or'cuts, such as benzol, toluol, solvent naphtha, and motor fuel, is alsocontemplated.

It will be readily seen that by means of my present invention doubleutilization of the caustic originally supplied for dephenolization isobtained. The alkalinity of this solution after its carbonation in thespringing tank is entirely suitable for use in the neutralization ofacid-Washed light oil, or fractions thereof, and by springing thephenolate before its use for this purpose a very high grade of phenolsis obtained. Thus it is possible to effect the economy resulting fromdouble utilization of the alkalinity required in either of theseprocesses, without the disadvantage of impairing the quality ordiminishing the quantity of tar acids recovered.

It will be obvious to those skilled in the art that variousmodifications can be made in the several parts of my apparatus and theseveral steps of my process without departing from Vthe spirit of myinvention and it is my intention to cover in the claims suchmodifications as are included Within the scope thereof.

I claim as my invention:

l. In the recovery of by-.products from coal distillation gas, theprocess comprising separating out tar acids and light oil from the coaldistillation gas, separating out these tar acids With a sodium hydroxidesolution by passing carbon dioxide gas therein, thereby liberating thetar acids and forming sodium carbonate, and immediately using theresulting carbonate solution to neutralize said light oil which hasfirst been treated with sulphuric acid.

2. In the recovery of by-products from fuel gas containing tar acids,the process comprising separating out tar acids and light oil from fuelgas containing the same, separating out these tar acids With a sodiumhydroxide solution by passing carbon dioxide gas therein, therebyliberating the tar acids and forming sodium carbonate, and immediatelyusing the resulting carbonate solution to neutralize said light oilwhich has first been treated with sulphuric acid.

IRVIN H. JONES.

